In present informational society, people usually wish to receive useful information conveniently whenever and wherever. Therefore, various portable wireless communication devices are widespread in people's daily lives. In a wireless device, an antenna which is used to transmit and receive radio waves so as to transfer radio signals is undoubtedly one of the very important elements. For a variety of handhold terminal devices, an antenna does not only need to be lightweight, thin and small in size, but also has to be preferably operated at a dual-frequency, and the frequency band has to be wider.
Currently, handhold terminal devices typically use a plurality of frequency bands to realize multiple functions or auxiliary functions, such as the frequency bands required by Global System for Mobile Communication (GSM) and Digital Cellular System (DCS) for a cell phone, an ultra-high frequency (UHF) for an interphone as well as the frequency for Global Positioning System (GPS), etc. Correspondingly, the antenna thereof is of a dual-frequency or a multiple-frequency. In the prior art, dual-frequency antennas mostly use a dual-frequency antenna having a dual array structure. FIG. 1 shows a schematic structural view of a dual-frequency antenna with a dual array structure in the prior art, wherein two portions on both sides of the feed point have a whip antenna structure and a planar helical structure respectively so as to form different resonant frequencies.
In the prior art, a dual-frequency antenna having a partial resonant structure is often used. In the partial resonant structure, a higher frequency band is typically designed in accordance with different structural parameters and the whole antenna array generates a kind of frequency, while high frequency resonance is generated by helices having different parameters, such as early cell phone antennas in which DCS frequency band is processed at the bottom of coil.
Currently, most external dual-frequency antennas are realized by a partial resonant structure. This is accomplished by a helical structure in which a high frequency resonant portion is placed at the bottom of coil and cooperates with another portion to form resonance at a lower frequency. However, in the prior art, for an external dual-frequency antenna of an interphone which operates at the working mode of UHF+GPS frequency band, a GPS resonant portion is placed at the bottom of helical so as to form resonance, as shown in FIG. 2. In this kind of design for a GPS frequency band, the performances of antenna are more concentrated on the lower half of sphere, while the performances on the upper half of sphere (the portion directing towards the sky) required by GPS are poor. Therefore, this design is not suitable for professional GPS performances and the function orientation of professional terminal devices. Moreover, in this kind of design for UHF frequency band, the bandwidth of antenna is not large enough. If a wide frequency UHF+GPS antenna (e.g., 380-430 MHz) having the same length is required, it is very hard to be achieved by this kind of design. The bandwidth in the UHF frequency band is relatively narrow under the influence of GPS frequency band. Therefore, there is a need for a dual-frequency antenna which not only has a good GPS directivity, but also has a wider bandwidth at ultra-high frequency.